Bifunctional Squaramide Organocatalysts for the Asymmetric Addition of Formaldehyde tert-Butylhydrazone to Simple Aldehydes.

The nucleophilic addition of formaldehyde tert-butylhydrazone to simple aldehydes (a formal hetero-carbonyl-ene reaction) can be performed with good reactivity and excellent enantioselectivity by virtue of the dual hydrogen-bonding activation exerted by amide-squaramide organocatalysts. The resulting hydroxydiazenes (azo alcohols) were isolated in high yields as enantiomerically enriched azoxy compounds after a regioselective azo-to-azoxy transformation. Subsequent derivatization provides an entry to relevant amino alcohols, oxazolidinones, and derivatives thereof.